Core Assemblies for Magnetic Saturation Detector Without Requirement for DC Bias Current

This application is a continuation of U.S. patent application Ser. No. 17/622,178, filed on Dec. 22, 2021, now pending, which is a National Stage Entry of International Application No. PCT/US2020/046621 filed on Aug. 17, 2020, which claims priority from U.S. Provisional Application No. 62/888,194, filed Aug. 16, 2019, hereby incorporated by reference in their entirety.

This patent application is related to patent application 62/887,810, entitled, “Magnetic Saturation Detector with Single and Multiple Transverse Windings,” and to patent application 62/888,089, entitled, “Energy Transfer Element Including A Communication Element,” each of which is filed on even date herewith, each of which is assigned to the common assignee, and each of which has one common inventor. Each of the Related Applications is incorporated herein by reference in its entirety.

The disclosure describes embodiments of magnetic core assemblies for an inductive element, useful for providing a voltage on a transverse winding of the inductive element. The voltage may be monitored to produce a signal that directly indicates the onset of magnetic saturation in the inductive element, without the need for a bias current in the transverse winding.

Efforts have been made to enable a flyback power supply, or other power product that comprises an inductive energy transfer element, to deliver maximum output power by extending the available flux density of its coupled inductor to include the saturation flux density under a variety of electrical and thermal conditions.

Known applications use a transverse winding of an inductive element to detect impending magnetic saturation by processing a voltage signal that appears between the terminals of the transverse winding. A control circuit may respond to the voltage signal on the transverse winding to operate the power supply safely near the maximum available flux density of the magnetic material.

A shortcoming of previous implementations of a transverse winding to detect impending magnetic saturation is that they require current in a transverse winding. The current produces a transverse magnetic field that changes in response to the saturation characteristics of the magnetic material. The changing transverse magnetic field is accompanied by a changing electric field that is observed as a voltage between the terminals of the transverse winding. The need to provide a bias current in a transverse winding increases complexity of the circuits, reduces efficiency of the power supply, and typically adds cost to the product. Therefore, there is a need for an innovation that produces a signal that directly indicates magnetic saturation without the shortcomings described above.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention.

Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or subcombinations in one or more embodiments or examples. Particular features, structures or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings are not necessarily drawn to scale.

1 FIG. 1 FIG. 100 102 104 148 154 144 146 IN O is a schematic diagramof an example power supply configured to operate with a magnetic saturation detector that uses a single transverse winding that requires no bias current in the transverse winding. The example power supply ofreceives an input voltage Vwith respect to an input returnand provides a regulated output to a load. The regulated output may be a voltage Vwith respect to an output return, a current Io, or a combination of both.

1 FIG. 1 FIG. 104 144 120 118 122 128 118 122 128 106 118 110 118 104 1 2 1 1 2 1 1 1 The example power supply ofuses a flyback power converter to produce an output that is galvanically isolated from the input. In other words, a voltage applied between the input returnand the output returnwould produce negligible current. The flyback power converter in the example power supply ofincludes an energy transfer element L1that has an input power winding P, output power winding P, and single transverse winding T. Power windings Pand Ptake part principally in the transfer of energy between the input and the output, whereas transverse winding Ttakes part in the detection of magnetic saturation. A clamp circuitis coupled across the input power winding P. An input switch S1is coupled between the input power winding Pand the input return.

132 152 134 112 110 132 108 110 114 132 110 108 132 110 120 S1 S1 In operation, an input-referenced controllerreceives signals from an output-referenced controllerthrough a galvanic isolatorto produce a drive signalthat opens and closes the input switch S1. An open switch cannot conduct current, whereas a closed switch may conduct current. The input-referenced controllersenses current Iin the input switch S1as a current sense signal. In one mode of operation, input-referenced controllermay open input switch S1when the current Ireaches a threshold value. In another mode of operation, the input-referenced controllermay open input switch S1when energy transfer element L1reaches a state of impending magnetic saturation.

110 116 124 118 122 120 106 110 124 122 136 138 154 146 148 154 146 150 152 132 134 110 134 P1 P2 1 2 1 2 P2 2 O O O O O The switching of switch S1produces pulsating currents Iand Iin the respective power windings Pand Pof energy transfer element L1, as well as pulsating voltages Vand Vacross those respective windings. Clamp circuitprevents excess voltage on input power switch S1when the switch opens. Output winding current Ifrom output power winding Pis rectified by diodeand filtered by output capacitor Cto produce an output voltage Vand an output current Iat a load. Either the output voltage V, the output current I, or a combination of both may be sensed as an output sense signalby the output-referenced controller. The output-referenced controller compares the sensed output quantity to a reference value, and may communicate with the input-referenced controllerthrough a galvanic isolator circuitto switch the input switch S1appropriately to obtain the desired output values. The galvanic isolator circuitmay include any of the many known ways use to use optical, magnetic, and capacitive technologies to couple signals between galvanically isolated circuits.

1 FIG. 1 T1 1 128 120 130 128 In the example power supply of, transverse winding Tmay respond to a transverse magnetic flux density within energy transfer element L1, producing transverse voltage Von transverse winding Tto indicate magnetic saturation.

2 FIG. 1 FIG. 2 FIG. 1 FIG. 2 FIG. 200 207 227 225 218 118 122 257 1 2 is a perspective drawingthat illustrates the salient features of an example energy transfer element with similarities to an energy transfer element that may be used in the example power supply of. The example energy transfer element inis constructed from two RM-style ferrite core-pieces. An upper core Ref. member, e.g. upper core-half, is assembled over a lower core member, e.g. lower core-half. Each magnetic core-half has a center postsurrounded by a windingthat represents one or more power windings, such as Pand Pin. In a practical component the turns of the power windings typically would be placed on a separate spool, sometimes referred to as a bobbin or a coil former, that would fit over the center posts to facilitate assembly.shows a gapin the center post of the assembled core-halves. The dimension of the gap is typically selected along with the number of turns on the power windings to set the electrical parameters desired for a particular application. In some applications, the gap contains a permanent magnet to provide a flux density offset to the flux density produced by current in a power winding. The gap may be achieved either with identical top and bottom core-halves having center posts of the same length, or with one core-half that has a center post shorter than the center post of the other core-half. Alternatively, a spacer consisting of an electrically insulating material with relatively low magnetic permeability may be inserted between identical core-halves to distribute the gap among the three vertical structural features. A gap in the center post is immaterial to the detection of magnetic saturation. As such, illustrations in this disclosure may show structures with and without gaps in a center post to emphasize that a gap in a center post is not required to practice the invention.

2 FIG. 228 247 237 218 247 228 also shows a transverse windingthat passes through an aperturein the center postof each core-half such that the transverse winding is perpendicular to the power winding. The aperturein the center of the center post of each core-half is an off-the-self option in some offerings of RM-style cores that come with a center hole that accommodates a ferrite slug to adjust the inductance of the power winding after assembly. Transverse windingsmay traverse the adjustment hole in place of the ferrite slug to provide for a magnetic saturation detector in accordance with the teaching of this invention. Other styles of ferrite cores may have apertures for other purposes, such as for example assembly hardware, that may be suitable for a transverse winding. In cores that do not come with a suitable aperture, a hole may be drilled through the center post. It is appreciated that a transverse winding need not be geometrically perpendicular to the power winding. Any conductor that passes completely through a turn of a power winding in one direction at any angle may be a transverse winding.

T1 T T 230 255 255 2 FIG. The transverse winding is typically a single turn, although a transverse winding may include more than one turn to amplify the voltage Von the winding that is produced by a changing transverse flux density as the magnetic material of the core begins to saturate. The example ofshows a transverse current Ithat introduces a transverse flux density to detect magnetic saturation. The alternative core assemblies described in this disclosure do not require the transverse current Ito detect magnetic saturation.

2 FIG. 2 FIG. 257 It will be appreciated by those skilled in the art that magnetic assemblies and parts of magnetic assemblies may be described by various terms that are not necessarily technically accurate nor precise. For example, virtually any piece of magnetic material may be referred to as a magnetic core. A complete assembly of pieces of magnetic components exclusive of windings may also typically be referred to as a magnetic core. Assemblies of magnetic cores typically comprise of two core pieces. In many assemblies of magnetic cores, such as in the example of, the two core pieces may be nearly identical. Hence, each piece may be commonly referred to as a core member or core-half. In practice, the gap in a center post, such as the gapin the assembly offor example, may be formed by removing material from the center post of only one of two identical core-halves. Each piece is still referred to as a core-half even though the piece that forms the gap is no longer identical to the piece that had no material removed. The assembly may be further referred to as a core pair. In this disclosure the term core-half may be used to refer to one of two nearly identical pieces in an assembly to distinguish the assembly from alternative assemblies comprising pieces that are obviously not identical. For example, an assembly of two E-shaped pieces may have the same geometrical features and magnetic properties as an assembly that uses one E-shaped piece with one I-shaped piece. The EE assembly comprises two core-halves whereas the EI assembly does not, although each assembly comprises two core members. It is noted that in the practice of the art each one of a magnetic core piece, a magnetic core member, a magnetic core element, a magnetic core-half, and a magnetic core assembly may be referred to as a magnetic core.

3 FIG. 2 FIG. 3 FIG. 2 FIG. 3 FIG. 300 307 327 377 387 307 327 218 216 355 328 365 307 327 328 355 355 330 328 330 P1 P P T T P P P P T P T T T P T P T T T is a perspective drawingof the structure ofshowing an upper core-halfand a lower core-halfwith no windings. Reference marksandhighlight identical features on the upper core-halfand lower core-halfrespectively that are useful in discussion of the relative positions of the two core-halves. The windings are removed into avoid obscuring annotations of flux density vectors. A power winding encircling the center post and conducting current, such as for example windingand current Iin, would produce a power flux density Bwithin the assembly as illustrated by the vectors Bannotated in. A current Iin a transverse winding represented schematically by the pathwould produce a transverse flux density represented by vectors Bthat are perpendicular to the power flux density vectors Bin the center post and in most parts of the assembly outside the center post. Furthermore, contributions from transverse components of the power flux density Bin the upper half-coreare cancelled by contributions from transverse components of the power flux density Bin the lower half-core, so that the net contribution with respect to the pathis zero. In other words, the geometry of the assembly is such that vectors Bof power flux density are orthogonal to vectors Bof transverse flux density with respect to the path of a transverse winding. As such, changes in power flux density Bproduce negligible voltage on a transverse winding. The transverse current Iis typically constant to introduce constant transverse magnetic field that produces a transverse flux density B. The transverse flux density Bis forced to change as the magnetic material begins to saturate. As the vector sum of the power flux density Band the transverse flux density Bincreases to reach a saturation flux density of the magnetic core, further increase in power flux density Bforces a change in transverse flux density Bthat produces a transverse voltage Vbetween the terminals of a conductor in the path. The transverse voltage Vmay be processed and interpreted to detect the onset of magnetic saturation.

4 FIG. 4 FIG. 3 FIG. 4 FIG. 4 FIG. 4 FIG. 3 FIG. 4 FIG. 3 FIG. 4 FIG. 3 FIG. 400 407 427 477 487 377 387 477 487 377 387 is an annotated perspective drawingillustrating an example magnetic core assembly that does not require a bias current in a transverse winding to detect magnetic saturation. The example ofdoes not show a power winding nor a gap in the center post to avoid distracting from the essential features of the invention. The examples inandboth use RM-style ferrite core-halves. In the example of, the upper core-halfis rotated approximately 30 degrees clockwise about its center when viewed from the top with respect to the lower core-half. The rotational offset ofis in contrast to the traditional assembly depicted inthat has vertical edges of the upper and lower core-halves aligned such that the vertical edges are collinear and the flat vertical faces are co-planar. The displacement inmay be gauged also by the locations of the reference marksandthat correspond to the respective features highlighted by the reference marksandin. The reference marksandare not vertically aligned inwhile in the traditional assembly in, the reference marksandare vertically aligned. The rotational displacement between the two core-halves may be considered a skewing feature in the assembly of the magnetic cores that allows a magnetic saturation detector to determine the onset of magnetic saturation by monitoring the voltage on a transverse winding in the absence of a current in a transverse winding.

4 FIG. 4 FIG. 407 427 428 430 430 shows flux density vectors B with both horizontal and vertical components in the vertical sides of the structure even though there is no transverse current to introduce a transverse magnetic field into the assembly. The rotational offset between the upper core-halfand the identical lower core-halfintroduces transverse components in the flux density vectors B. The geometry of the assembly ofensures that for any orientation of a transverse winding in the paththat passes through the aperture in the center post, there will be a net magnetic flux density passing through the surface bounded by the conductor that is the transverse winding. That is, there will be a net magnetic flux density passing through the loop formed by the transverse winding when the transverse winding has no current. A change in the transverse component of flux density will produce a voltage between the terminals of the transverse winding. In other words, a change in the transverse component of flux density induces a non-zero transverse voltage VTon a transverse winding that may be processed to indicate impending magnetic saturation. The saturation characteristics of the magnetic material of the energy transfer element produce features in the waveform of the transverse voltage VTthat allow detection of magnetic saturation during the operation of a power supply.

5 FIG.A 5 FIG.B 5 FIG.A 1 FIG. 5 FIG.A 500 116 P1 andgraphically illustrate the relationships between magnetic flux density in an energy transfer element and the current in a power winding of the energy transfer element.is a graphA that shows magnetic flux density plotted on the vertical axis with respect to a power winding current such as for example Iin the power supply ofon the horizontal axis. More accurately, the horizontal axis represents the sum of the ampere turns of all power windings, not just the current in a single power winding. The example energy transfer element for the graph ofhas no flux density offset from a permanent magnet, so the flux density is at zero when the current is at zero.

505 505 535 525 505 535 505 515 515 505 535 505 5 FIG.A 1 FIG. P1 QL MAX MAX SAT SAT SAT QL MAX SAT MAX SAT KNEE KNEE SAT The magnetic flux density curveinhighlights several distinguishing features. The curvetakes on positive and negative values with symmetry about the origin on both axes. There is positive flux density for positive current and negative flux density for negative current. Features are emphasized for positive values of current in the graph because the current in the example circuit ofis in only one direction. As the current Iincreases from zero, the energy transfer element operates in a quasi-linear region Buntil the current reaches a maximum value Ithat corresponds to the upper boundaryof the quasi-linear region. The slope of the curvein the quasi-linear regionis positive and relatively constant. In other words, the flux density increases with increasing current at a nearly constant ratio. As the current increases beyond I, the slope of the flux density curvedecreases, reaching a lower relatively constant value for currents greater than a saturation current Ithat corresponds to a saturation flux density B. It is important to detect operation at the saturation flux density Bbecause operation at higher values of flux density is likely to produce current that may damage switching devices and other components in a power supply. As the slope of the curvechanges from its nearly constant value in the quasi-linear region Bwhere the current is less than Ito its much lower nearly constant value where the current is greater than I, there is region where the slope is changing rapidly between the two relatively constant values. The current between Iand Iwhere the slope of the flux density is changing most rapidly is identified as Isince it corresponds to the relatively sharp bend in the flux density curve. A magnetic saturation detector may indicate operation at the flux density corresponding to current Iso that operation at currents greater than Imay be avoided.

5 FIG.B 1 FIG. 5 FIG.A 5 FIG.B 500 116 P1 is a graphB that shows magnetic flux density plotted on the vertical axis with respect to a power winding current such as for example Iin the power supply ofon the horizontal axis. In contrast to the graph of, the example energy transfer element for the graph ofhas a flux density offset from a permanent magnet.

505 555 515 535 257 545 5 FIG.A 5 FIG.B 2 FIG. 5 FIG.B SAT QL OFFSET P1 The flux density offset from the permanent magnet shifts the curveofto the right on the horizontal axis as shown by the curvein. The values on the vertical axis for the saturation flux density Band the quasi-linear region Bare unchanged because they are intrinsic properties of the magnetic material of the core. A flux density offset can change the relationship between the flux density and an external stimulus, but it cannot change the intrinsic properties of the magnetic material. The flux density offset from a permanent magnet, such as for example one that may be placed in the gapof the assembly illustrated in, is shown inas Bthat produces a negative flux densityin the energy transfer element when the current Ion the horizontal axis is zero.

525 535 515 QL SAT MAX SAT KNEE MAXBIAS SATBIAS KNEEBIAS KNEEBIAS SATBIAS 5 FIG.A 5 FIG.B The flux density offset increases the values of the current Ipi required to reach the upper boundaryof the quasi-linear region B, the saturation value B, and the flux density where the slope of the curve is changing most rapidly. In other words, currents I, I, and Iofare respectively increased to I, I, and Iin. Therefore, in energy transfer elements that use a permanent magnet to provide a flux density offset, the magnetic saturation detector may indicate operation at the flux density corresponding to current Iso that operation at currents greater than Imay be avoided.

6 FIG. 1 FIG. 600 116 610 130 620 P1 T1 is a graphthat shows a waveform of current in a power winding and a waveform of voltage on a transverse winding from an example energy transfer element that may operate in the example power supply of. Current Iis plotted on the vertical axisand transverse voltage Vis plotted on vertical axis, both with respect to time on the horizontal axis.

IN 1 T1 1 102 118 120 110 130 128 The current is the result of the input voltage Vacross power winding Pof energy transfer element L1when switch S1closes and opens. The transverse voltage Von transverse winding Tarises from a mechanism that exploits the magnetic saturation characteristic of the magnetic material to produce a voltage on a transverse winding.

The saturation characteristic describes the behavior of the total flux density that is produced by current in a power winding. The flux density is in general not uniform throughout a magnetic core assembly. The flux densities in some parts of the assembly may be greater than flux densities in other parts of the assembly. Therefore, some parts of the assembly may reach the saturation flux density before other parts of the assembly reach the saturation flux density.

247 3 FIG. In an ordinary magnetic core assembly that has an aperture in a center post such as the aperturein the example of, the vectors of flux density from current in a power winding are generally perpendicular to the vectors of flux density from current in a transverse winding.

4 FIG. As shown by the example of, the geometry of the magnetic core assembly may be configured to rotate the vector of the total flux density so that the magnetic flux density vector may contain two components, even when the flux density is within the quasi-linear region. The vectors of the two components of the flux density are perpendicular to each other in the magnetic material. One of the components may be a transverse component that induces a voltage in a transverse winding.

T1 Flux density vectors must follow closed paths. The geometry of the magnetic core assembly forces the transverse component of the flux density vector to take a path of higher magnetic reluctance than the path of the flux density vector that is perpendicular to it. An increase in current in the power winding forces the sum of the two components of flux density to increase in magnitude, even when the total flux density is near the saturation value. As the material saturates, its reluctance to the flux density increases. The flux density in the material along the lower reluctance path is higher than the flux density in the material along the higher reluctance path. Since the saturation characteristic imposes a limit on the increase of the sum of the two vectors, the vector with the higher magnitude on the lower reluctance path will increase at a lower rate than the vector with the lower magnitude along the higher reluctance path. The result is an effective additional rotation of the flux density vector that increases the component of flux density in the transverse direction, producing a rapid increase in the voltage Vbetween the terminals of the transverse winding.

QL PP PP T1 PP T1 P1 555 5 FIG.A 5 FIG.B 6 FIG. When the total flux density is in the quasi-linear region (Binand), the transverse flux density is approximately proportional to the principal flux density, and voltage on the power windings produces a voltage on the transverse windings that is approximately proportional to the voltages on the power windings, represented inas the voltage Vwhile the power winding is conducting current. Since the voltage Vis approximately proportional to the voltage on the power windings, it is a known value that may be taken into consideration when processing the transverse voltage Vto detect magnetic saturation. Alternatively, magnetic saturation may be determined in a manner that ignores the presence of V, such as for example by detecting a change in the sign of the slope of the Vwhile the current Iis increasing. Thus, features of the time-varying voltage on the transverse winding may be interpreted to detect magnetic saturation in the energy transfer element.

6 FIG. 1 FIG. 5 FIG.A 6 FIG. 110 630 525 535 132 110 118 122 118 122 1 1 2 P1 MAX QL 2 1 MAX 2 MAX 1 T1 2 2 3 2 4 3 4 To produce the example waveforms of, switch S1in the example power supply ofcloses at time t. Between time tand time t, current Iincreases from zero to the value I, and the flux density increases from zero to the upper boundaryof the quasi-linear region Bof the flux density characteristic shown inwhen input-referenced controlleropens the switch. When switch S1opens at time t, current in power winding Pgoes from Ito zero while current in power winding Pincreases from zero to a value required to maintain the flux density that corresponds to current Iin winding power winding P. The transverse voltage Vchanges polarity at time tbecause the changing flux density that produces the voltage on the windings decreases after the switch opens, whereas the flux density increases while the switch is closed. In the example of, the currents in the power winding Pdecreases to zero at time tbetween time tand time t. The voltage remains at zero between time tand time tsince the flux density is not changing in that interval.

110 630 640 650 132 630 535 660 680 640 670 650 132 4 P1 MAX KNEE SAT P1 MAX QL TI T1 5 P1 KNEE T1 P1 KNEE SAT T1 7 When switch S1closes again at time t, current Iagain increases from zero, rising to exceed both Iand I, reaching Ibefore the input-referenced controlleropens the switch. As the increasing current Iexceeds I, the flux density leaves the quasi-linear range B, and transverse voltage Vrapidly becomes more positive with a substantial positive slope. The transverse voltage Vattains a maximum positive valueat time tthat corresponds to current Iat I. The transverse voltage Vbecomes less positive with a substantial negative slopeas current Ipasses through Iand approaches its final value of Iat time to, where input-referenced controlleropens the switch. Transverse voltage Vbecomes more negative and reaches a maximum negative value as the current in the power windings decreases to zero at time tbetween time to and time to.

7 FIG. 6 FIG. 700 5 6 is an expanded viewof the waveforms inshowing greater detail near times tand t. The expansion emphasizes the characteristics of the transverse voltage waveform that allow a circuit to detect magnetic saturation from observation of the voltage on a transverse winding.

7 FIG. 7 FIG. 680 640 680 T1 P1 KNEE shows an extremumin the waveform of the transverse voltage Vwhen current Iis at the value I. Although the extremumis a peak in the example of, the polarity of the voltage on the transverse winding may be reversed simply by interchanging the two ends of the winding at the voltage sensing terminals or by reversing the direction of the angular displacement between the upper and lower core-halves in the assembly by turning the upper core-half anticlockwise instead of clockwise with respect to the lower core-half when viewed from the top to make the extremum a valley instead of a peak.

5 5 5 5 5 5 7 FIG. 660 670 A characteristic of the extremum that is independent of the polarity is the change in the sign of the slope of the waveform from before the time tto after the time t.shows a positive slope on the portionbefore tand a negative slope on the portionafter t. The change in sign of the slope of the voltage on the transverse winding is an indication of magnetic saturation. If the polarity of the transverse winding were reversed, the slope would be negative before tand positive after t. The change in sign of the slope is also independent of the magnitude of the extremum. Since the slope of the transverse voltage waveform changes sign, either going from positive to negative or going from negative to positive, the slope of the transverse voltage waveform must pass through a value of zero. Therefore, a zero-crossing detector that observes the slope of the voltage on the transverse winding may detect magnetic saturation. A controller that opens a switch in a power winding in response to a zero-crossing detector that senses the voltage on a transverse winding may control a power supply to operate at its maximum power capability without damage. In practice, to avoid false indications of magnetic saturation, the zero-crossing detector may be gated to observe the voltage on the transverse winding only after the switch has been closed for a threshold time or only when the current in the switch is greater than a threshold current.

QL 535 The preceding examples have illustrated the application of a magnetic saturation detector in a power supply with a power converter that operates in discontinuous conduction mode (DCM). That is, in each switching period the current in the power windings and the flux density in the energy transfer element (with no flux density offset) start at a value of zero and end at a value of zero. In contrast, under different conditions of input voltage, output voltage, and load, a power supply may operate its power converter in continuous conduction mode (CCM). That is, in CCM the current in the power windings and the flux density (again with no flux density offset in the energy transfer element) does not start and end at a value of zero in each switching period. The operation of the magnetic saturation detector in CCM is the same as the operation in DCM when in each CCM switching period the flux density starts and ends within the quasi-linear region B.

T T Consider that the flux density with a transverse component takes a path of a greater distance, and therefore higher reluctance, than the path of flux density that has no transverse component. Hence, before saturation the flux density with transverse components will be lower in magnitude than the flux density without transverse components. The part of the magnetic core assembly with the lower-reluctance path and higher flux density begins to saturate first. Saturation increases reluctance. The growing reluctance diverts additional increase in flux density to the transverse path that is not yet saturated, increasing the voltage V. When there is saturation in both paths, the transverse component of flux density increases at a lower rate, causing Vto decrease.

8 FIG. 6 FIG. 7 FIG. 800 843 857 813 833 853 863 830 828 843 853 863 830 828 LR HR T LR HR LR HR T is a planar modelof a magnetic core assembly for a magnetic saturation detector that does not require a bias current in a transverse winding. The model is useful to explain the waveforms ofand. One portion of the model represents a center postwith a gap, wrapped with a power windingthat is driven by a time-varying current I(t) from a current source. The magnetic field from the current in the power winding produces a flux density B in the center post. A second portion of the model represents a lower-reluctance pathfor a flux density B. A third portion of the model represents a transverse path of higher reluctancefor a transverse flux density Bthat may induce a transverse voltage Vin a transverse winding. Flux density B from the magnetic field in the center postdivides into flux densities Band B. The flux density Bin the lower-reluctance path will be larger than the flux density Bin the higher-reluctance transverse path if the core material is in its quasi-linear region. The portion of the core with higher flux density will saturate before the portion of the core with lower flux density. As the lower-reluctance pathbegins to saturate, its reluctance increases, shifting more of the total flux density B to the higher-reluctance path, and increasing the voltage Von transverse winding.

9 FIG. 4 FIG. 9 FIG. 4 FIG. 9 FIG. 9 FIG. 4 FIG. 9 FIG. 900 928 907 927 937 907 947 930 928 T is a perspective drawingof another example magnetic core assembly with a transverse windingthat does not require a bias current in the transverse winding to detect magnetic saturation. As in, the gap in the center post and power windings around the center post are not shown into avoid obscuring features of the invention. In contrast to the example of, the example ofhas no rotational offset between the upper core-halfand the lower core-half: the vertical edges of the upper and lower core-halves are aligned such that the vertical edges are collinear and the flat vertical faces are co-planar. Both core-halves inare modified from the standard RM-style shown inby the removal of material from each core-half.shows regionsin the upper core-halfwhere material that formed features in the standard configuration has been removed. Those standard features are still present in the regions. The lower core-half is identical to the upper core-half. The removal of material also removes a degree of symmetry in the geometry of the assembly to introduce a component of transverse flux density that produces a transverse voltage Von the transverse windingwhen there is voltage on a power winding that encircles the center post. The removal of material from standard core-halves may be considered a skewing feature in the assembly of the magnetic cores that allows a magnetic saturation detector to determine the onset of magnetic saturation by monitoring the voltage on a transverse winding in the absence of a current in a transverse winding.

10 FIG. 9 FIG. 9 FIG. 10 FIG. 1000 is an annotated perspective drawingof the example magnetic core assembly ofshowing paths of flux densities from current in a power winding. As in, the gap in the center post and power windings around the center post are not shown into avoid obscuring features of the invention.

10 FIG. 4 FIG. 4 FIG. 10 FIG. 10 FIG. 928 930 930 T T shows flux density vectors B with both horizontal and vertical components in the vertical sides of the structure even though there is no transverse current to introduce a transverse magnetic field into the assembly. The asymmetry in the assembly introduced by removal of material from upper and lower core-halves introduces transverse components in the flux density vectors B, similar to the rotational offset shown in the example of. As in the example configuration of, the geometry of the assembly ofensures that for any orientation of a transverse windingthat passes through the aperture in the center post, there will be a net magnetic flux density passing through the surface bounded by the conductor that is the transverse winding. That is, there will be a net magnetic flux density passing through the loop formed by the transverse winding when the transverse winding has no current. A change in the transverse component of flux density will produce a voltage between the terminals of the transverse winding. The geometry of the example assembly ofalso creates a path of higher magnetic reluctance for the transverse component of flux density with respect the non-transverse component of flux density. In other words, a change in the transverse component of flux density induces a non-zero transverse voltage Von a transverse winding that may be processed to indicate impending magnetic saturation. The saturation characteristics of the magnetic material of the energy transfer element produce features in the waveform of the transverse voltage Vthat allow detection of magnetic saturation during the operation of a power supply.

11 FIG. 11 FIG. 11 FIG. 1100 1128 1107 1127 1128 is a perspective drawingof yet another example magnetic core assembly with a transverse windingthat does not require a bias current in the transverse winding to detect magnetic saturation.shows an upper core-halfand a lower core-halfthat have modifications to a standard EE-style geometry. Inthe core-halves are separated, and the windings are not shown to give better visibility to the features of the geometry. In practice, the upper and lower core-halves would be in contact, and the center post may include a gap. There is also a hole drilled through the center post to form an aperture that accommodates the transverse winding.

11 FIG. The example of, one corner is removed from each outer leg of each core-half. Two corners that are farthest apart in a top view of the standard half-core geometry are removed. The two core-halves are assembled with an orientation such that a leg with a full corner mates with a leg that has a corner removed.

12 FIG. 11 FIG. 10 FIG. 12 FIG. 4 FIG. 11 FIG. 1200 1130 T is an annotated perspective drawingof the example magnetic core assembly ofshowing paths of flux densities from current in a power winding. As in,shows flux density vectors B with both horizontal and vertical components in the vertical sides of the structure even though there is no transverse current to introduce a transverse magnetic field into the assembly. The asymmetry in the assembly introduced by removal of material from upper and lower core-halves introduces transverse components in the flux density vectors B, similar to the rotational offset shown in the example of. As in the previous examples, the transverse components of flux density produce a transverse Vthat may be processed to detect magnetic saturation. It will be appreciated that variants of the standard EE-style, such as for example the common EI-style, may be modified by removal of material from the E-piece and the I-piece as suggested by, where the I-piece is analogous to the plate that is common to the center and outer legs of each core-half.

13 FIG. 14 FIG. 15 FIG. Modifications of the center posts of standard assemblies may introduce a transverse component of flux density to produce a voltage on a transverse winding that occupies an aperture in the center post. Examples of such modifications are shown in,, and. Modifications may be considered skewing features that allow a magnetic saturation detector to determine the onset of magnetic saturation by monitoring the voltage on a transverse winding in the absence of a current in a transverse winding.

13 FIG. 13 FIG. 13 FIG. 1300 is an annotated perspective drawingof a portion of a magnetic core assembly with emphasis on a center post showing paths of flux densities from current in a power winding.also includes a diagram illustrating the relationship between a Cartesian rectangular coordinate system using X, Y, Z coordinates and a cylindrical coordinate system using r, θ, Z coordinates. The cylindrical coordinate system may be more useful than the rectangular coordinate system to describe the salient features of the configuration shown in.

13 FIG. 180 1328 1130 T The center post of the structure inhas a rectangular cross section that rotatesdegrees from the lower plate to the upper plate of the structure. Such a structure would have a helical reluctance path in the center section. A transverse windingpasses through an aperture that is a hole through the center of the post parallel to the Z axis to produce transverse voltage Vbetween the ends of the winding. Coils that may form input and output power windings of either a transformer or an energy transfer element may surround the center post.

13 FIG. 13 FIG. shows example flux density vectors that may arise from the excitation of windings surrounding the center post. The flux density vectors may form closed paths through other portions of the structure not shown in, passing from the ends of the top plate to the ends of the bottom plate and returning through the center post.

13 FIG. L H L 1339 1349 1339 The example ofshows two flux density vectors in the center post. A linear flux density vector Btakes a vertical path that is the shortest distance and lowest reluctance path between the bottom plate and the top plate. A helical flux density vector Bhas a component in the θ direction and a component in the Z-direction as it follows a path of greater reluctance than the path of Bbetween the bottom plate and the top plate.

L H 1339 1349 The linear flux density vector Bis expected to have a greater magnitude than the helical flux density vector Bsince the magnetic reluctance is greater for the helical path than for the linear path.

T L T L H T 1330 1328 1339 1330 1339 1328 1349 1328 Changes in the magnitude of the θ-component of the helical flux density vector in the center post produce a transverse voltage Vat the ends of the transverse windingthat passes through the aperture in the center post. A change in the linear flux density vector Bdoes not make a significant contribution to the transverse voltage Vsince the linear flux density vector Bis parallel to the transverse windingin the center post. A change in the helical flux density vector Bcontributes to the voltage Vsince it encircles the transverse winding.

T T T T 1330 1330 1330 1330 The transverse voltage Vmay indicate magnetic saturation in the center post. For increasing flux in the center post, the material in the lower-reluctance linear path saturates before the material in the helical path. When saturation causes the reluctance of the linear path to increase, the flux density along the helical path increases, producing an increase in the transverse voltage V. The transverse voltage Vdecreases when the helical path saturates, producing a reversal of slope in the transverse voltage Vthat may be interpreted to detect magnetic saturation.

14 FIG. 13 FIG. H L H T 1449 1439 1449 1430 1428 In a practical structure, the center post would have approximately twice the cross-sectional area of the top and bottom plates so that the flux density would be nearly the same through the structure.is a variant of the structure ofwith a square cross section for the center post that has approximately twice the cross-sectional area of each plate. Flux density vectors B in the top and bottom plates sum in the center post to form helical flux density vector Band linear flux density vector B. Changes in the transverse component of helical flux density vector Bproduce a transverse voltage Vat the ends of a transverse windingthat may be processed and interpreted to detect magnetic saturation.

15 FIG. 15 FIG. 1500 is an annotated perspective drawingof a portion of yet another magnetic core assembly with emphasis on a center post showing paths of flux densities from current in a power winding. The structure illustrated inhas a round cylindrical center post with grooves that define a helical reluctance path. A round cylindrical center post with grooves may be a preferred feature in an assembly for a magnetic saturation detector that does not require bias current in a transverse winding.

H L H T T 1549 1539 1549 1530 1528 1530 15 FIG. Flux density vectors B in the top and bottom plates sum in the center post to form helical flux density vector Band linear flux density vector B. Changes in the transverse component of helical flux density vector Bmay produce a transverse voltage Vat the ends of a transverse windingthat may be processed and interpreted to detect magnetic saturation. It is not necessary for the helical path to rotate multiple times around the center post as illustrated in. A partial rotation of the helical path about the center post may be sufficient to produce a transverse voltage Vto detect magnetic saturation.

Embodiments of the present disclosure include configurations of magnetic cores for energy transfer elements that include features for a magnetic saturation detector in which a magnetic energy transfer element includes at least one transverse winding and at least one power winding. Current in a power winding produces a magnetic flux density in the assembly. The geometry of the assembly of magnetic cores of the energy transfer element provides a path of lower magnetic reluctance for a principal component of the flux density and a path of higher magnetic reluctance for a transverse component of the flux density that is substantially perpendicular to the principal component of the flux density. A saturation detector circuit senses a voltage between terminals of the transverse winding to indicate a condition of magnetic saturation at an extremum of the time-varying voltage on the transverse winding. A bias current is not required in the transverse winding for the transverse component of the flux density to produce a voltage between the terminals of the transverse winding. In other words, configurations of magnetic cores may introduce a transverse component of flux density in the absence of current in the transverse winding such that a voltage on the transverse winding may indicate a condition of magnetic saturation.

The above description of illustrated examples of the present invention, including what is described in the Abstract, are not intended to be exhaustive or to be limitation to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it is appreciated that the specific example voltages, currents, frequencies, power range values, times, etc., are provided for explanation purposes and that other values may also be employed in other embodiments and examples in accordance with the teachings of the present invention.

Although the present invention is defined in the claims, it should be understood that the present invention can alternatively be defined in accordance with the following examples:

Example 1: A magnetic core assembly comprising: a core assembly comprising, a lower core piece having a center section, and an upper core piece having a center section, the center section of the upper core piece aligned to the center section of the lower core piece such that a center post of the core assembly is formed; and a power winding, wrapped around the center post, wherein when a current is passed through the power winding a power flux density vector is generated, wherein the power flux density vector has a transverse component and a non-transverse component, and wherein the transverse component has a higher magnetic reluctance than the non-transverse component.

Example 2: The magnetic core assembly as in example 1 wherein the lower core piece comprises a lower core member; and the upper core piece comprises an upper core member.

Example 3: The magnetic core assembly as in example 2, wherein each core member has a reference mark, the reference marks are rotationally offset within the core assembly, and the rotational offset introduces the transverse component to the power flux density vector.

Example 4: The magnetic core assembly as in example 2, wherein the lower and upper core members each includes a skewing feature and a reference mark.

Example 5: The magnetic core assembly as in example 4, wherein for each core member, the skewing feature is positioned at the core member perimeter and the reference marks are aligned within the core assembly.

Example 6: The magnetic core assembly as in example 1, wherein at least one of the lower and upper core members has a skewing feature, and the skewing feature introduces the transverse component to the power flux density vector.

Example 7: The magnetic core assembly as in example 6, wherein the skewing feature is a truncated corner.

Example 8: The magnetic core assembly as in example 6, wherein the center post includes the skewing feature.

Example 9: The magnetic core assembly as in example 8, wherein the skewing feature comprises a helix.

Example 10: The magnetic core assembly as in example 8, wherein the skewing feature comprises grooves on the surface of the center post.

Example 11: A magnetic saturation detector comprising the magnetic core assembly as in example 1, the magnetic saturation detector further comprising: a transverse winding, perpendicular to the power winding, wherein transverse components from the magnetic core assembly produce a transverse voltage waveform on the transverse winding; and a voltage detection circuit, configured to receive the transverse voltage waveform and to detect a change in the sign of the slope of the transverse voltage waveform, wherein the change in the sign of the slope indicates magnetic saturation.

Example 12: The magnetic saturation detector as in example 11, wherein the center post has an aperture and the transverse winding is positioned within the aperture.

Example 13: The magnetic saturation detector as in example 12, wherein each of the lower core member and the upper core member each comprises a core member having a reference mark, wherein the reference marks are rotationally offset within the core assembly, and wherein the rotational offset introduces transverse components to the power flux density vector.

Example 14: The magnetic saturation detector as in example 12, wherein the lower core member and the upper core member, each comprises a core member having a skewing feature and a reference mark, wherein the reference marks are aligned within the core assembly, and the skewing feature introduces transverse components to the power flux density vector.

Example 15: The magnetic saturation detector as in example 14, wherein the skewing feature is positioned at the center post and is selected from a group consisting of helixes and surface grooves.

Example 16: The magnetic saturation detector as in example 14, wherein for each core member, the skewing feature is positioned at the perimeter of the core member.

Example 17: The magnetic saturation detector as in example 16, wherein the skewing feature is a truncated corner.

Example 18: A power supply that includes the magnetic saturation detector, as in example 12, comprising: an output-referenced controller, coupled to the magnetic core assembly and configured to sense an output sense signal, compare the output sense signal to a reference value, and generate a switching signal; and an input-referenced controller, coupled to the magnetic core assembly and configured to produce a drive signal.